A mobile communication system supporting an LTE (Long Term Evolution) scheme is capable of performing CA (Carrier Aggregation) by using a Pcell (Primary Cell) which is a serving cell in a PCC (Primary Component Carrier) and an Scell (Secondary Cell) which is a serving cell in an SCC (Secondary Component Carrier).
Moreover, the mobile communication system supporting the LTE-Advanced scheme is configured to perform TA (Timing Advance) control.
Specifically, as shown in FIG. 5, in the TA control, a radio base station eNB is configured to specify a TA value for each of mobile stations UE #1 and UE #2 while the mobile stations UE #1 and UE #2 are configured to adjust the transmission timings of their uplink signals on the basis of their specified TA values so that the reception timings (EFT timings) at which the radio base station eNB receives the signals from the multiple mobile stations UE #1 and UE #2 can be the same.
For example, as shown in FIG. 5, the radio base station eNB causes the mobile station UE #2 located at the edge of a cell to transmit its uplink signal at a timing earlier than that of the mobile station UE #1 located at the center of the cell.
Meanwhile, in a case of performing Inter-band CA (UL CA) with cells of different frequencies, the cells differ from each other in radio characteristics (delay characteristics and attenuation characteristics). Thus, for the cells having different radio characteristics, it is necessary to perform TA control in a suitable manner for each of the radio characteristics.
Specifically, as shown in FIG. 6, in a case of performing Inter-band CA in a mobile communication system supporting the LTE-Advanced scheme, a Pcell and Scells #1 to #3 are grouped into groups of equivalent radio characteristics (TAGs: Timing Adjustment Groups), and TA control is performed on a group basis.
This TA control is called “Multiple Timing Advances (MTA) control.”
Note that these groups include two types of groups—a pTAG including the Pcell (TAG-A in the example of FIG. 6) and an sTAG including only Scells (TAG-B in the example of FIG. 6).